Passivity/Lyapunov based controller design for trajectory tracking of flexible joint manipulators

A passivity and Lyapunov based approach for the control design for the trajectory tracking problem of flexible joint robots is presented. The basic structure of the proposed controller is the sum of a model-based feedforward and a model-independent feedback. Feedforward selection and solution is analyzed for a general model for flexible joints, and for more specific and practical model structures. Passivity theory is used to design a motor state-based controller in order to input-output stabilize the error system formed by the feedforward. Observability conditions for asymptotic stability are stated and verified. In order to accommodate for modeling uncertainties and to allow for the implementation of a simplified feedforward compensation, the stability of the system is analyzed in presence of approximations in the feedforward by using a Lyapunov based robustness analysis. It is shown that under certain conditions, e.g., the desired trajectory is varying slowly enough, stability is maintained for various approximations of a canonical feedforward

Deeply subducted continental fragments - Part 2: Insight from petrochronology in the central Sesia Zone (western Italian Alps)

Subducted continental terranes commonly comprise an assembly of subunits that reflect the different tectono-metamorphic histories they experienced in the subduction zone. Our challenge is to unravel how, when, and in which part of the subduction zone these subunits were juxtaposed. Petrochronology offers powerful tools to decipher pressure–temperature–time (P–T–t) histories of metamorphic rocks that preserve a record of several stages of transformation. A major issue is that the driving forces for re-equilibration at high pressure are not well understood. For example, continental granulite terrains subducted to mantle depths frequently show only partial and localized eclogitization. The Sesia Zone (NW Italy) is exceptional because it comprises several continental subunits in which eclogitic rocks predominate and high-pressure (HP) assemblages almost completely replaced the Permian granulite protoliths. This field-based study comprises both main complexes of the Sesia terrane, covering some of the recently recognized tectonic subunits involved in its assembly; hence our data constrain the HP tectonics that formed the Sesia Zone. We used a petrochronological approach consisting of petrographic and microstructural analysis linked with thermodynamic modelling and U–Th–Pb age dating to reconstruct the P–T–t trajectories of these tectonic subunits. Our study documents when and under what conditions re-equilibration took place. Results constrain the main stages of mineral growth and deformation, associated with fluid influx that occurred in the subduction channel. In the Internal Complex (IC), pulses of fluid percolated at eclogite facies conditions between 77 and 55 Ma with the HP conditions reaching  ∼  2 GPa and 600–670 °C. By contrast, the External Complex (EC) records a lower pressure peak of  ∼  0.8 GPa for 500 °C at  ∼  63 Ma. The juxtaposition of the two complexes occurred during exhumation, probably at  ∼  0.8 GPa and 350 °C; the timing is constrained between 46 and 38 Ma. Mean vertical exhumation velocities are constrained between 0.9 and 5.1 mm year−1 for the IC, up to its juxtaposition with the EC. Exhumation to the surface occurred before 32 Ma, as constrained by the overlying Biella Volcanic Suite, at a mean vertical velocity between 1.6 and 4 mm year−1. These findings constrain the processes responsible for the assembly and exhumation of HP continental subunits, thus adding to our understanding of how continental terranes behave during subduction

COMMENT ON "THE ROLE OF H3O+ IN THE CRYSTAL STRUCTURE OF ILLITE" BY F. NIETO, M. MELINI, AND I. ABAD

The arguments of Nieto et al. (2010) in favor of the incorporation of H3O+ rather than H2O in interlayer positions of illite are disputable. Stoichiometric arguments suggest that the excess water in the Silver Hill illite is in the form of H2O. Moreover, recent thermodynamic models assuming the incorporation of interlayer H2O in illite provide reasonable estimates of temperature and water content using the AEM/TEM analyses of Nieto et al. (2010)

Pervasive fluid-rock interaction in subducted oceanic crust revealed by oxygen isotope zoning in garnet

Dehydration reactions in the subducting slab liberate fluids causing major changes in rock density, volume and permeability. Although it is well known that the fluids can migrate and interact with the surrounding rocks, fluid pathways remain challenging to track and the consequences of fluid-rock interaction processes are often overlooked. In this study, we investigate pervasive fluid-rock interaction in a sequence of schists and mafic felses exposed in the Theodul Glacier Unit (TGU), Western Alps. This unit is embedded within metaophiolites of the Zermatt-Saas Zone and reached eclogite-facies conditions during Alpine convergence. Chemical mapping and in situ oxygen isotope analyses of garnet from the schists reveal a sharp chemical zoning between a xenomorphic core and a euhedral rim, associated to a drop of ~ 8‰ in δ18O. Thermodynamic and δ18O models show that the large amount of low δ18O H2O required to change the reactive bulk δ18O composition cannot be produced by dehydration of the mafic fels from the TGU only, and requires a large contribution of the surrounding serpentinites. The calculated time-integrated fluid flux across the TGU rocks is 1.1 × 105 cm3/cm2, which is above the open-system behaviour threshold and argues for pervasive fluid flow at kilometre-scale under high-pressure conditions. The transient rock volume variations caused by lawsonite breakdown is identified as a possible trigger for the pervasive fluid influx. The calculated schist permeability at eclogite-facies conditions (~ 2 × 10–20 m2) is comparable to the permeability determined experimentally for blueschist and serpentinites

REE and Hf distribution among accessory phases in H and CK chondrites.

第2回極域科学シンポジウム/第34回南極隕石シンポジウム 11月17日（木） 国立国語研究所 2階講

OH incorporation and retention in eclogite-facies garnets from the Zermatt–Saas area (Switzerland) and their contribution to the deep water cycle

The incorporation mechanisms of OH groups in garnet were investigated in a suite of high-pressure rocks from the Zermatt–Saas area (Switzerland) using a combination of Fourier transform infrared spectroscopy (FTIR) and electron probe micro-analysis (EPMA). Investigated garnet specimens include grossular–andradite–uvarovite solid solutions in serpentinite and rodingite and almandine–grossular–pyrope–spessartine solid solutions in eclogite, mafic fels and meta-sediment. All rocks experienced the same peak metamorphic conditions corresponding to a burial depth of ∼ 80 km (∼ 540 ∘C, 2.3 GPa), allowing determination of the OH content in garnet as a function of rock type. The capacity for OH incorporation into garnet strongly depends on its composition. Andradite-rich (400–5000 µg g−1 H2O) and grossular-rich garnet (200–1800 µg g−1 H2O) contain at least 1 order of magnitude more H2O than almandine-rich garnet (&lt; 120 µg g−1 H2O). Microscale analyses using FTIR and EPMA profiles and maps reveal the preservation of OH zoning throughout the metamorphic history of the samples. The OH content correlates strongly with Mn, Ca and Ti zoning and produces distinct absorption bands that are characteristic of multiple nano-scale OH environments. The use of 2D diffusion modelling suggests that H diffusion rates in these rocks is as low as log(D[m2 s−1]) = −24.5 at 540 ∘C. Data were collected for the main garnet-bearing rock types of the Zermatt–Saas area allowing a mass balance model of H2O to be calculated. The result shows that ∼ 3360 kg H2O km−1 (section of oceanic crust) yr−1 could be transported by garnet in the subducting slab beyond 80 km depth and contributed to the deep-Earth water cycle during the Eocene subduction of the Piemonte–Liguria Ocean.</p

Diachronous evolution of the alpine continental subduction wedge: evidence from P-T estimates in the Briançonnais Zone houillère (France - Western Alps).

International audienceThe study of continental subduction processes requires detailed Pressure Temperature (P-T) paths to understand the kinematic of burial and exhumation of continental units. In the French Western Alps, the Briançonnais zone is a remnant of the continental subduction wedge. P-T conditions have been estimated in its most internal parts, but there is a lack of data in the western part, known as the "Zone houillère". This Briançonnais Zone houillère is classically divided into two sub-units: the upper and lower Houiller units. This study focuses on both of these in the Clarée valley, north of Briançon. In this low-grade metamorphic terrain, estimation of P-T history is complicated because there are few adapted methods and these rocks have a poor metamorphic mineralogical content, including detrital metamorphic minerals inherited from their hercynian history. Therefore, to acquire accurate P-T estimates a multi-method approach is required, involving qualitative and quantitative Raman study of Carbonaceous Material (RSCM), chemical analysis from quantified X-ray maps and thermodynamic modelling of chlorites and K-white micas. Such multi-approach P-T estimates on a sandstone sample allow distinguishing hercynian peak metamorphic conditions of 371 ± 26°C and 3.5 ± 1.4 kbar and alpine peak metamorphic conditions of 275 ± 23°C and 5.9 ± 1.7 kbar. These results are consistent with our RSCM and Tmax estimates. Raman study conducted on organic-rich schist samples shows an eastward increase of the alpine Tmax in the upper Houiller unit, from 280 to 300°C across the Briançonnais Zone houillère. In contrast, carbonaceous material included in detrital grains of muscovite in the sandstone exhibits higher temperatures. This hercynian Tmax is estimated using thermodynamic modelling at 376 ± 50°C. According to these results and previous work in more internal parts of the Briançonnais zone, a geodynamic reconstruction is proposed, which is characterized by a diachronous evolution of the Briançonnais zone involved in alpine continental subduction at different times. The geothermal gradient in the Briançonnais zone changes from 8°C/km during early continental subduction, to 40°C/km during the collisional event at about 35-30 Ma. The intermediate gradient of 15°C/km estimated in the Briançonnais Zone houillère suggests that this unit was buried later, than the more internal Briançonnais units, after 40 Ma

Tracing fluid infiltration into oceanic crust up to ultra-high-pressure conditions

Fluid–rock interaction within the altered oceanic crust and across the slab–mantle boundary during subduction facilitates element transfer, but the dynamics of fluid transport and fluid–rock exchange during upward fluid migration are still unclear. A study of metamorphic fluid–rock interaction within a section of subducted oceanic crust was carried out on eclogites and metasediments of the ultra-high-pressure Lago di Cignana Unit (NW Italian Alps). The P–T modeling of a quartzschist shows that garnet grew during the prograde and sporadically during the retrograde path and that phengite mainly records the peak to retrograde conditions. Microscale geochemical analysis of garnets has revealed a systematic evolution of oxygen isotopic composition with garnet major element zonation, with extreme within-sample core–rim variations in δ18O between 18 and 4‰ providing evidence for external fluid influx. Garnet in eclogites and calcschists, as well as garnet cores in quartz-rich lithologies, shows normal compositional zoning, as expected for prograde garnet growth, and a relatively constant oxygen isotopic composition. The outer garnet growth zones within a few metasediments show reverse or discontinuous zoning and progressively lower δ18O. Despite major element zoning, the isotopic composition of mica is homogeneous across chemical zoning in one eclogite and one quartzschist, but shows 6‰ variability in another quartzschist. In the underlying Zermatt–Saas serpentinites, antigorite from nine serpentinite samples shows some variation in δ18O, with average δ18O values for individual samples ranging from 1 to 6‰. These results provide evidence for two main stages of external fluid infiltration: (i) fluids from the dehydration of mafic lithologies entered the sequence at peak conditions around 3 GPa, as indicated by the oxygen composition of intermediate zones of mica and garnet, and (ii) low δ18O fluids from serpentinites infiltrated parts of the sedimentary package during exhumation prior to 1.5 GPa, as recorded by the 4‰ garnet outer rims. Samples recording external fluid infiltration are concentrated in the lower part of the sequence, indicating channelized fluid flow, suggesting focused fluid infiltration due to permeability contrasts between metasedimentary and eclogitic lithologies. Channelized fluid flow in the ultra-high-pressure metasediments of Lago di Cignana has not resulted in systematic decarbonation of the metasediments

The role of the antigorite + brucite to olivine reaction in subducted serpentinites (Zermatt, Switzerland)

Metamorphic olivine formed by the reaction of antigorite + brucite is widespread in serpentinites that crop out in glacier-polished outcrops at the Unterer Theodulglacier, Zermatt. Olivine overgrows a relic magnetite mesh texture formed during ocean floor serpentinization. Serpentinization is associated with rodingitisation of mafic dykes. Metamorphic olivine coexists with magnetite, shows high Mg# of 94–97 and low trace element contents. A notable exception is 4 µg/g Boron (> 10 times primitive mantle), introduced during seafloor alteration and retained in metamorphic olivine. Olivine incorporated 100–140 µg/g H2O in Si-vacancies, providing evidence for low SiO2-activity imposed by brucite during olivine growth. No signs for hydrogen loss or major and minor element diffusional equilibration are observed. The occurrence of olivine in patches within the serpentinite mimics the former heterogeneous distribution of brucite, whereas the network of olivine-bearing veins and shear zones document the pathways of the escaping fluid produced by the olivine forming reaction. Relic Cr-spinels have a high Cr# of 0.5 and the serpentinites display little or no clinopyroxene, indicating that they derive from hydrated harzburgitic mantle that underwent significant melt depletion. The enrichment of Mg and depletion of Si results in the formation of brucite during seafloor alteration, a pre-requisite for later subduction-related olivine formation and fluid liberation. The comparison of calculated bulk rock brucite contents in the Zermatt-Saas with average IODP serpentinites suggests a large variation in fluid release during olivine formation. Between 3.4 and 7.2 wt% H2O is released depending on the magnetite content in fully serpentinized harzburgites (average oceanic serpentinites). Thermodynamic modelling indicates that the fluid release in Zermatt occurred between 480 °C and 550 °C at 2–2.5 GPa with the Mg# of olivine varying from 68 to 95. However, the majority of the fluid released from this reaction was produced within a narrow temperature field of < 30 °C, at higher pressures 2.5 GPa and temperatures 550–600 °C than commonly thought. Fluids derived from the antigorite + brucite reaction might thus trigger eclogite facies equilibration in associated metabasalts, meta-gabbros, meta-rodingites and meta-sediments in the area. This focused fluid release has the potential to trigger intermediate depths earthquakes at 60–80 km in subducted oceanic lithosphere. © 2020, The Author(s).ISSN:1661-8734ISSN:1661-872